1. Field of the Invention
The present invention relates to an image-forming apparatus and more particularly to a process cartridge of an electrophotographic image-forming apparatus.
2. Description of the Related Art

As is well known, the electrophotographic image-forming apparatus carries out developing of an electrostatic latent image formed on a photoconductive medium by using toner and outputting the developed image, i.e., toner image by transferring the toner image on the photoconductive medium into a printing paper.
Such electrophotographic image-forming apparatus has a photoconductive medium, a light-exposing unit to form an electrostatic latent image on the photoconductive medium, a developing unit to develop an electrostatic latent image, a transferring unit to transfer the developed image onto a paper, a fixing unit to fix the transferred image on the paper, and a paper-feeding/discharging unit.
There are a variety of rollers required to constitute the photoconductive medium and the developing unit, and the rollers are degraded in performance over time, causing image degradation. Accordingly, these rollers require periodic replacement. Additionally, toner is a consumable and should be supplied in time when used up.
The process cartridge is designed to make the replacement process simple and convenient by incorporating elements such as a variety of rollers of the photoconductive medium and the developing unit and a predetermined amount of toners, all having similar lifespan, into one part as a cartridge.
FIG. 1 is a cross-sectional view of an inner structure of the general process cartridge, and FIGS. 2A and 2B are left side and right side perspective views, respectively.
Referring to FIG. 1, a reference numeral 10 refers to a cartridge frame. As shown in FIG. 1, the cartridge frame 10 has a toner reservoir 11 and a toner recovery part 12. The photoconductive medium 20 is positioned between the toner reservoir 11 and the toner recovery part 12 of the frame 10. The developing roller 31 is installed in the cartridge frame 10, maintaining a predetermined developing nip with respect to the photoconductive medium 20. The toner supplying roller 32 is installed in the cartridge frame 10 to supply toner to the developing roller 31. In FIG. 1, the reference numerals 33, 41, and 42 represent an agitator, a charging roller, and an auxiliary charging roller, respectively, and the reference numerals 43, and 44 represent a doctor blade and a cleaning blade, respectively.
As shown in FIGS. 2A and 2B, the process cartridge has first and second plates 50 and 51 joined on both sides of the cartridge frame 10, supporting both ends of the shafts of respective rollers installed in the cartridge frame 10, including the photoconductive medium 20, the developing roller 31, the toner supplying roller 32, the agitator 33, the charging roller 41, and the auxiliary charging roller 42.
First through fourth guiding protuberances 50a, 50b, 51a, and 51b are formed on the first and the second plates 50 and 51 to provide guidance during attachment/ detachment of the process cartridge to and from the image-forming apparatus. More particularly, the first and the third guiding protuberances 50a and 51a are formed in register with the photoconductive medium shaft 20a, and the second and the fourth guiding protuberances 50b and 51b are formed apart from the first and the third guiding protuberances 50a and 51a by a predetermined distance.
Referring to FIG. 3, a cartridge mounting part 61, on which the process cartridge is mounted, is provided to a main body frame 60 of the image-forming apparatus, and the cartridge mounting part 61 has a guide rail 61a, which is inclined a predetermined angle, and an seating part 61b, having a substantially semicircular shape.
With such a configuration, when the process cartridge is mounted on the main body frame 60 of the image-forming apparatus, the first through the fourth guiding protuberances 50a, 50b, 51a, and 51b, formed on the first and the second plates 50 and 51 of the process cartridge, enter by sliding on the guiding rail 61a. Then, as shown in FIG. 4, the first and the third guiding protuberances 50a and 51a settle down on the seating part 61b, whereby the photoconductive medium is normally grounded and mounted.
In dismounting the process cartridge from the main body frame 60 of the image-forming apparatus to replace the process cartridge, the process cartridge is drawn in the direction of the arrow in FIG. 5A, and accordingly, the first and the third guiding protuberances 50a and 51a are rotated in the direction of the arrow as shown in FIG. 5B with the second and the fourth guiding protuberances 50b and 51b acting as a hinge point, moving out of the seating part 61b of a semicircle shape, so that the process cartridge may be separated through the process as shown in FIG. 5C.
However, since, in the above-described general process cartridge of the image-forming apparatus, the first through the fourth guiding protuberances 50a, 50b, 51a, and 51b to guide attachment/detachment of the process cartridge, are integrally formed on the first and the second plates 50 and 51, which are joined to both sides of the cartridge frame 10, the following problems may be generated.
The first and the second plates 50 and 51 are assembled to the cartridge frame 10 by way of a screw fastening operation. Upon assembling of the first plate 51 (e.g., on the right side), a force C to rotate the plate 51 in the screw rotating direction, is generated as shown in FIG. 6A of the cartridge. Such rotational force C of the plate 51 pushes out the developing roller 31 to rotate in the clockwise direction with the seen direction used for the reference, while in contact with a side of the photoconductive medium 20. But, upon assembling of the second plate 50 (left side), as shown in FIG. 6B, since the developing roller 31 is rotated in the counterclockwise direction with the seen direction used for the reference, the rotational direction of the developing roller 31 is forced to rotate in a direction opposite to the screw rotating direction. Namely, a force D is generated, causing a rotation of the plate 50 toward the direction in which the developing roller 31 is separated from the photoconductive medium 20.
Such rotation of the first and the second plates 50 and 51 in the assembling process causes non-uniformity in right and left developing nips between the photoconductive medium 20 and the developing roller 31. This results in, irregular densities in right and left portions of an image and a difference in developing amounts at right and left sides. Accordingly, lifespans of right and left parts, including the roller in the cartridge, are different, and image output becomes irregular. In a serious case, the photoconductive medium 20 and the developing roller 31 partially disengage, causing the white-void on the image.
Also, the rotation of the plates 50 and 51 may generate deformation of the cartridge frame 10 and may cause aging of the photoconductive medium 20 and the roller 31, whereby serious image problem may result.
Also, in the conventional process cartridge, upon assembling, the plates 50 and 51 are assembled with a photoconductive medium shaft 20a used for the reference, but aligning all parts to be assembled using such one reference point is difficult.
Also, there is no way to check the error if the dimensions of the projecting portions of the plates 50 and 51, such as the distance between the first guiding protuberance 50a and the second guiding protuberance 50b or the distance between the third guiding protuberance 51a and the fourth guiding protuberance 51b are formed inaccurately during the manufacturing process, and the process cartridge may be incorrectly mounted on the main body frame of the image-forming apparatus.